VIDEO TRANSCRIPT
Macadamia harvesting with sweepers and blowers: effect on soil movement

(Narrator) Macadamia nuts that drop to the orchard floor along the tree row, are out of the normal harvest zone for conventional finger wheel harvesters. That’s why harvest aids such as blowers are used to move nut from under the tree, towards the pick up zone. Sweepers are a later innovation, also used to move nut from out underneath the trees. Over time growers have observed signs of soil loss and root exposure underneath the tree rows after years of blower use. Sweepers are perceived by industry to move less soil but this has never been confirmed. Soil scientist Justine Cox from NSW DPI in collaboration with the macadamia industry, wanted to find out just how much soil was being moved as a result of these two harvest practices.

(Justine Cox – Soil Scientist) We set up an experiment to measure how much soil was moved underneath the tree row by blowers and sweepers. We found that blowers moved more soil than sweepers. Blowers moved 2.5 tonne a hectare per year, while sweepers moved 1.3 tonne per hectare per year, at an 8 by 4 spacing. The pattern was different too. Blowers moved soil a lot further away from the tree row while sweepers created a depression in the sweepers’ path.

(Narrator) This steady loss of soil under the trees is not sustainable. There is a need to change management practices, if we are to continue to use these types of harvest methods

(Doug Rowley - grower) I’ve had experience with both. My first harvester had a blower on it and it always concerned me the amount of material that was being moved by the blower. I then changed my harvester to a lower impact harvester and put a sweeper on that and was delighted with the difference in the material that was being moved under the tree. The important thing with using a sweeper is the speed of the harvesting. You have to go fast enough to flip the nuts out and at the same time have a speed on the sweeper head which isn’t going to scour the dirt, the material that’s underneath the trees.  Most of our trees we’ve got smothergrass growing up to the butt so we keep it well mown and we find that the sweeper works very successfully over the smothergrass picking the nuts out and throwing them into the front of the harvester. The main advantage of smothergrass on this farm is the speed with which we can get back into the orchard after rain. We’ve never been delayed more than 48 hours after significant rain events before we can get the harvester back in. The other advantage is the smothergrass means that we have got very little soil loss from the orchard and because we keep it well mown we actually have no down side in terms of getting the nuts out of the tree line and in front of the harvester, so its just win win.

(Narrator) So how can we reduce soil movement?
sweep or blow over groundcovers or mulch
if you use a blower, set the angle of the blower horizontal to the soil surface
in the case of a sweeper, set the height to just above the soil level
and in both cases, use appropriate ground speed

On bare soil, blowers and sweepers will continue to contribute to soil movement. We can minimise soil loss by careful harvester setup and operation. With a protective groundcover such as smothergrass, we may be able to eliminate it all together.